The present invention relates to systems for controlling the rate at which fluent, particulate materials are fed through a trough by an auger feed mechanism. More particularly, the invention relates to feed rate control systems responsive to the instantaneous weight of the delivered material at the discharge end of a trough.
Systems for controlling the feed rate of solid, fluent materials are generally classed as either volumetric or gravimetric. In a volumetric feed control system, probably the more common of the two, material is fed or dispensed in terms of volume per unit of time, e.g., cubic inches per minute, etc. Volumetric feeders are dependent on a consistent bulk density of the material for an accurate and uniform feed rate. If feeding at a uniform weight rate, e.g., lbs./hr., oz./min., g./min., etc., is required, a gravimetric system must be used. The present invention is a gravimetric type feed control system, assuring uniform weight distribution or constant weight rate independent of changing bulk density of the feed stock being dispensed.
Many, if not most, gravimetric feeders are of the so-called loss-in-weight type. In some, the material is fed via a belt, and in others by an auger or feed screw. Commonly, the weight of the supply hopper and its contents and sometimes the belt or auger as well, is noted at regular intervals and the feed rate (belt or auger speed) is adjusted as necessary to maintain the desired weight dispensing rate. Consequently, volumetric feed control is normally used while the hopper is being filled, or when there is significant shaking or machine vibration. This may cause appreciable errors when the feed stock is of very low density (e.g., less than 5 lbs./cu.ft.) and subject to changing bulk density, since significant fill time may be required for the relatively large hoppers necessary to handle sufficient weight of the low density material to register on a scale.
The large components required in loss-in-weight feeders for low density material cause such feeders to be very sensitive to external machine and building vibration. This vibration problem, coupled with the relatively long hopper fill time, requires operation in a volumetric control mode for times which are unacceptably long when dispensing dry solids with a variable density distribution.
It is a principal object of the present invention to provide a simple, reliable and accurate gravimetric control system for dispensing fluent, dry solids at a desired rate.
A further object is to provide a gravimetric feed control which is especially suited for use with low density feed stock, such as certain plastic materials which are commonly provided in a flakelike form prior to being formed with heat and pressure into disposable plates, and other articles.
Another object is to provide a novel and improved system for feeding particulate solids through an open-topped trough with an auger in a gravimetrically controlled manner.
Other objects will in part be obvious and will in part appear hereinafter.